New (Integrated Laboratory Industry Research Program) · 2014. 3. 12. · k Ω· cm 2) f max =125.9 kHz f max =102.3 kHz 0 250 500 0-250-500 Z' (kΩ ·cm 2) 0.1 Hz 0 150 300 0-150-300

Managed by UT-Battelle for the Department of Energy

Project ID: ES157

Nancy Dudney (PI)

Oak Ridge National Laboratory

Contributors:

Wyatt Tenhaeff, Sergiy Kalnaus, Adrian Sabau, Erik Herbert

Vehicle Technologies Program Annual Merit Review and Peer Evaluation Meeting

May 2012

Composite Electrolyte to Stabilize Metallic Lithium Anodes

(Integrated Laboratory Industry Research Program)

“This presentation does not contain any proprietary, confidential, or otherwise restricted information”

2 Managed by UT-Battelle for the Department of Energy

Overview

• Timeline – Start October, 2011

• Technical barriers – Energy density (500-700 Wh/kg) – Cycle life, 3000 to 5000 deep

discharge cycles – Safety

• Budget – $300k FY12

• Partners – Oak Ridge National Laboratory

(lead) – Center for Nanophase Materials

Sciences, ORNL – University of Tennessee – SHaRE user facility, ORNL – Companies and collaborators for

electrolyte materials


Objectives and relevance

• Objectives: – Understand Li+ transport at interface between two dissimilar solid electrolytes,

e.g. ceramic/polymer – Develop composites of electrolyte materials with requisite electrochemical and

mechanical properties – Fabricate thin membranes to provide good power performance and long cycle life

• Relevance: – Enables implementation of Li metal anodes for high energy density chemistries

(e.g. Li-air, Li-S) – USABC has targeted a 5X improvement in energy density

Lithium anodes must be completely isolated from the electrolyte to prevent dendrites, side reactions and to stabilize the structure. Composites of multiple electrolytes may provide the needed combination of properties.


Milestones

Milestones: Target:

1. A composite electrolyte membrane <1mm thick where the internal interfaces do not significantly impede the Li ion transport.

October 2012

2. Simulation to estimate the ion conduction of an optimized composite structure. October 2012

3. Evaluate composite membrane with a lithium metal electrode for cycling stability and dc transport properties. October 2012


Approach 1. Develop methodologies to characterize both

electrochemical and mechanical properties including impedance spectroscopy and nanoindentation of thin films.

2. Characterize barriers to charge transport in laminated electrolyte structures, e.g. interfacial resistances, poor adhesion.

3. Demonstrate improved properties in composite electrolyte.

4. Simulate the optimal composite design.

5. Fabricate optimized, thin composite membranes with a lithium metal electrode to evaluate cycling stability and DC transport properties

Individual electrolytes

Bilayer composites

Dispersed composites

Optimized composites


Approach- Many electrolyte materials have been evaluated.

Polymer Electrolytes Notable Features PEO10:LiTFSI • High conductivity ( σ25°C = 2x10-6 S cm-1)

• Tmelt ≈ 35 °C • Slow crystallization kinetics

PEO16:LiCF3SO3 • Lower conductivity than PEO10:LiTFSI • Faster crystallization kinetics

PEO6:LiAsF6 -Sample from P. Bruce at University of St. Andrews (Scotland)

• 100% crystalline • Crystalline phase is conductive • Unity transference number

Ceramic and Glass Electrolytes Lithium phosphate oxynitride (Lipon) • Fabricated as thin film

• Chemically compatible with Li

Li1.3Ti1.7Al0.3(PO4)3 (LTAP) Sample from nGimat

• High conductivity • Chemically incompatible with Li

Ohara Nasicon-type (protected composition; crystal structure is similar to LTAP’s)

• High conductivity • Chemically incompatible with Li • Commercially available


Ionic conductivity is measured by impedance spectroscopy with blocking electrodes

0 2000

-200 25 °C 50 °C

-Z'' (

Ω·c

m2 )

Z' (Ω·cm2)

1 MHz

10 kHz1 MHz

10 kHz

1 kHz 252 kHz

631 kHz

0.0 12.50

-25

(kΩ

·cm

2 )

(kΩ·cm2)

0 125 250 375 5000

-125

-250-Z

'' (kΩ

·cm

2 )-Z

'' (kΩ

·cm

2 )

Z' (kΩ·cm2)

3.16 kHz

1 MHz

100 Hz

0.0 7.5 15.0 22.5 30.00.0

-7.5

-15.0

T=25 °C

(

) T=50 °C

1 MHz

100 kHz

1 kHz

Ohara PEO16:LiCF3SO3 PEO10:LiTFSI

Characteristic time scales of PEO10:LiTFSI and PEO16:LiCF3SO3 are very different enables a useful comparison of the interfacial impedances with Ohara ceramic

0 10 20 30 40 500

-25

-Z'' (

kΩ·c

m2 )

-Z'' (

kΩ·c

m2 )

Z' (kΩ·cm2)

39.8 kHz

251 Hz1 MHz

0.10 0.15 0.20 0.25 0.300.0

-0.1

T=25 °C

T=50 °C

79.4 kHz1 MHz


Conductivities of individual phases vary over several orders of magnitude

2.7 2.9 3.1 3.3 3.5

1E-7

1E-6

1E-5

1E-4

1E-3

PEO16:LiCF3SO3 Ohara PEO10:LiTFSI

T (°C)

σ (S

cm

-1)

1000/T (K-1)

90 80 70 60 50 40 30 20

Melting Temperatures PEO10:LiTFSI = 35 °C PEO16:LiCF3SO3 = 60 °C

Controlling reproducibility of polymer electrolytes is a challenge error bars.


Using laminated bilayer samples to characterize interfacial resistances between two dissimilar solid electrolytes

Laminated structures provided a well-defined interfacial area which enables quantitative characterization of interfacial impedances

Characterizing Li+ transport normal to the interface

Previous results from similar systems show that interfacial impedance is dominant

Abe, T. et al. J Electrochem Soc. 2004. Tenhaeff, W.E. et al. J Electrochem Soc. 2011. *Note: different ceramic *Note: different inorganic, polymer

The interfacial resistance must be minimized for conductivity enhancements in polymer–ceramic composites.

Previous results from similar systems show that interfacial impedance is dominant

Here polymer was solvent cast over Lipon glass. Interface adds resistance.

Abe cast polymer over polished and sintered LLT pellet.


Interfacial resistance is not observed in bilayers of Ohara glass ceramic and PEO16:LiCF3SO3

0 20 40 60 80 1000

-25

-50

T = 50 °C

-Z'' (

kΩ·c

m2 )

Z' (kΩ·cm2)

fmax = 5011 Hz

fmax = 5248 Hz

T = 25 °C

0 1 2 3 4 5 60

-1

-2

-3Experiment Predicted

-Z'' (

kΩ·c

m2 )

fmax=125.9 kHz

fmax=102.3 kHz

0 250 5000

-250

-500

Z' (kΩ·cm2)

0.1 Hz

0 150 3000

-150

-300

Z"A

0.1 Hz

Double layer capacitances of the blocking electrodes at low frequencies were not modeled in the predicted spectra above.

Here, the experimental impedance of the bilayer is compared with that predicted from the individual materials in series.


Interfacial Impedance in Ohara\PEO16:LiCF3SO3

Previous study

Unlike previous studies, the interfacial resistance between Ohara and PEO16:LiCF3SO3 is small and not statistically different from zero for most temperatures.

( ),interface composite exp Ohara polymer predictedR R R R= − +

2.7 2.9 3.1 3.3 3.5-1

0

1

Rin

terf /

(Rpo

ly + R

Oha

ra) pr

ed

1000/T (K-1)

Tenhaeff, W.E. et al. J Electrochem Soc. 2011.

Interfacial resistance is dominant at all temperatures.

interface Lipon polymerR R R> +


Approach: Novel nanoindentation technique is used to characterize the mechanical properties of electrolytes

• Enables the direct observation of the nanoindentation process

• Allows the measurement of air/moisture sensitive materials, e.g. polymer electrolytes, lithium, etc.

Nanoindentation inside the SEM:

Loading

Unloading

Electrolyte

Support

Nanoindentation was done in conjunction with our collaborators at the University of Tennessee, George Pharr and Erik Herbert.


Initial nanoindentation characterizations were performed on crystalline PEO samples from Peter Bruce (PEO6:LiAsF6)

Indenter at Peak Load

Indenter tip

Polymer electrolyte

Residual Impression

ID Composition Average Elastic Modulus, E (GPa)

A PEO6:LiASF6 0.96

B PEO6:(95% LiAsF6-5% LiTFSI) 1.5


Future Work • Continue characterizing interfacial impedances between polymers and newly

developed ceramic electrolytes through partnerships

• Fabricate polymer composite electrolytes with particulate phase composed of conductive ceramics – Characterize transport and mechanical properties

• Develop models to elucidate composite architectures with optimal properties

• Electrochemical and DC transport measurements for composite electrolytes with Li electrodes

Collaborations • Ceramic electrolytes supplied by: Ohara Corp. and nGimat

• Lab samples of ceramic electrolytes from: Jeff Sakamoto (Michigan State University)

• Lab samples of polymers from: Peter Bruce (University of St. Andrews, Scotland)


Summary • Relevance: Polymer composite electrolytes with Li+-conductive ceramic fillers will enable the

implementation of Li metal anodes for high energy density cells.

• Approach – A variety of polymeric and inorganic solid electrolytes are characterized – A unique nanoindentation technique is used to characterize the mechanical properties

of air and moisture sensitive materials – Simplified bilayer studies are performed to quantify interfacial resistances between two

solid electrolytes

• Accomplishments and progress – Showed that crystalline PEO has a relatively high elastic modulus (around 1 GPa),

which is several orders of magnitude higher than conventional amorphous polymer electrolytes

– Demonstrated negligible interfacial impedance across planar interfaces of Ohara (ceramic) and PEO-based electrolytes

• Future work – Develop polymer composites with both phases conducting Li cations, characterize

electrical and mechanical properties. Develop models to reveal optimal architectures. – Characterize stability and cycleability of polymer nanocomposites with Li metal

electrodes

Documents

New (Integrated Laboratory Industry Research Program) · 2014. 3. 12. · k Ω· cm 2) f max =125.9 kHz f max =102.3 kHz 0 250 500 0-250-500 Z' (kΩ ·cm 2) 0.1 Hz 0 150 300 0-150-300